Roemer, who was nominated by US President Barack Obama in May 2009, is expected to leave by June.

"Ambassador Roemer's departure is for personal, professional and family considerations," the US embassy said in a statement.

"When I accepted the job two years ago, I told President Barack Obama that I will serve for two years, but that family considerations would be the front and centre after that," Roemer said.

Roemer said that the US-India relationship is on a "positive historic trajectory" towards a global partnership.

"The horizons of our relationship truly no limits," he said.

The US envoy said his two sons will be leaving for college in the next 14 months and he would like his parents and in-laws to spend more time with his children.

Noting that he came as a diplomat and was leaving feeling part of a family, he said, "For me and for my entire family the two years have been a time of incredible experiences, warm friendship, meaningful partnership".

"The US-India relationship - what my friend President Obama calls the defining partnership of the 21st century - has progressed to the global stage. I am very proud to have led the team responsible for deepening and broadening the strategic partnership of this critical bilateral relationship, which isone of the cornerstones of our foreign policy.

"The US India relationship is on a positive historic trajectory towards a global partnership that is changing the way our two nations create economic opportunity for our citizens, educating the leaders of tomorrow, and ensuring safe and secure communities," he said.